Lump.
An example of the element Cerium

Lump.
This sample arrived with a full set of lanthanides at a time when I was missing europium, terbium, holmium, ytterbium, and of course lutetium.

This very kind donation from Max Whitby of The Red Green & Blue Company in England completed my element collection, to the extent that it gave me a plausible sample of every element one can plausibly have a sample of. (The Red Green & Blue Company is selling a periodic table collection containing similar samples of the same stuff, and if you want a ready-made collection of elements, that's the first place I would look.)